Zoom lens system

ABSTRACT

A zoom lens system includes at least two lens groups, and a negative first lens group is positioned at the most object-side of the zoom lens system. The negative first lens group includes a negative sub-lens group and a positive sub-lens group. The positive sub-lens group includes a positive lens element and a rearmost lens element of the negative first lens group. The rearmost lens element includes a plastic lens element having at least one aspherical surface. The zoom lens system satisfies the following conditions:  
     | f   1   /f   1B-2 |&lt;0.3  (1)  
     0.02&lt; D   1B-2   /fw&lt; 0.2  (2)  
     0.001&lt;D B1-B2   /fw&lt; 0.1  (3)  
     wherein  
     f 1 : the focal length of the negative first lens group;  
     f 1B-2 : the focal length of the rearmost lens element of the negative first lens group;  
     fw: the focal length of the entire the zoom lens system at the short focal length extremity;  
     D 1B-2 : the thickness of the rearmost lens element of the negative first lens group; and  
     D B1-B2 : the distance between the positive lens element and the rearmost lens element in the positive sub-lens group.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a miniaturized and low-cost zoomlens system having a half angle-of-view of approximately 38° at theshort focal length extremity and a zoom ratio of approximately 3.

[0003] 2. Description of the Prior Art

[0004] In a conventional wide-angle zoom lens system having a largeangle of view of 38° at the short focal length extremity, a first lensgroup is provided with a negative optical power (hereinafter, a negativefirst lens group), i.e., a negative-lead type zoom lens system, and thenegative first lens group generally includes a positive lens element, anegative lens element, and a positive lens element, in this order fromthe object. In the above-explained negative-lead type zoom lens system,a positive lens element is provided as the most object-side lens elementin order to correct distortion occurred in the negative direction;however, the diameter and the overall length of the negative first lensgroup increase, so that, further miniaturization becomes difficult.

[0005] On the other hand, there are examples of utilizing a hybrid lenselement in the negative first lens group in order to achieve furtherminiaturization; however, cost reduction is difficult.

SUMMARY OF THE INVENTION

[0006] The present invention provides a miniaturized and low-cost zoomlens system having a half angle-of-view of approximately 38° at theshort focal length extremity, and having a zoom ratio of approximately3.

[0007] According to an aspect of the present invention, there isprovided a zoom lens system including at least two lens groups, and anegative first lens group is positioned at the most object-side of thezoom lens system.

[0008] The negative first lens group includes a negative sub-lens groupand a positive sub-lens group, in this order from the object.

[0009] The positive sub-lens group includes a positive lens element andthe most image-side (a rearmost) lens element of the negative first lensgroup, in this order from the object.

[0010] The rearmost lens element includes a plastic lens element havingat least one aspherical surface.

[0011] The zoom lens system satisfies the following conditions:

|f ₁ /f _(1B-2)|<0.3  (1)

0.02<D _(1B-2) /fw<0.2  (2)

0.001<D _(B1-B2) /fw<0.1  (3)

[0012] wherein

[0013] f₁ designates the focal length of the negative first lens group;

[0014] f_(1B-2) designates the focal length of the rearmost lens elementof the negative first lens group;

[0015] fw designates the focal length of the entire the zoom lens systemat the short focal length extremity;

[0016] D_(1B-2) designates the thickness of the rearmost lens element ofthe negative first lens group; and

[0017] D_(B1-B2) designates the distance between the positive lenselement and the rearmost lens element of the positive sub-lens group.

[0018] The aspherical surface of the rearmost lens element is providedon the object-side surface thereof, and the aspherical surface can beformed so that the positive power becomes stronger, compared with aparaxial spherical surface, in a direction away from the optical axis.

[0019] The aspherical surface of the rearmost lens element is providedon the image-side surface thereof, and the aspherical surface can beformed so that the positive power becomes stronger, compared with aparaxial spherical surface, in a direction away from the optical axis.

[0020] The aspherical surface of the rearmost lens element of thenegative first lens group preferably satisfies the following condition:

−1<ΔV<−0.1  (4)

[0021] wherein

[0022] ΔV designates the amount of change of the distortion coefficientdue to the aspherical surface of the rearmost lens element of thenegative first lens group under the condition that the focal length atthe short focal length extremity is converted to 1.0.

[0023] The refractive index N_(1A) of a glass material of at least onenegative lens element of the negative object-side sub-lens group in thenegative first lens group can satisfy the following condition:

N _(1A<)1.66  (5)

[0024] The present disclosure relates to subject matter contained inJapanese Patent Application No. 2002-145089 (filed on May 20, 2002)which is expressly incorporated herein in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention will be discussed below in detail withreference to the accompanying drawings, in which:

[0026]FIG. 1 is a lens arrangement of a zoom lens system according to afirst embodiment of the present invention;

[0027]FIGS. 2A, 2B and 2C show aberrations occurred in the lensarrangement shown in FIG. 1 at the short focal length extremity;

[0028]FIGS. 3A, 3B and 3C show aberrations occurred in the lensarrangement shown in FIG. 1 at an intermediate focal length;

[0029]FIGS. 4A, 4B and 4C show aberrations occurred in the lensarrangement shown in FIG. 1 at the long focal length extremity;

[0030]FIG. 5 is a lens arrangement of a zoom lens system according to asecond embodiment of the present invention;

[0031]FIGS. 6A, 6B and 6C show aberrations occurred in the lensarrangement shown in FIG. 5 at the short focal length extremity;

[0032]FIGS. 7A, 7B and 7C show aberrations occurred in the lensarrangement shown in FIG. 5 at an intermediate focal length;

[0033]FIGS. 8A, 8B and 8C show aberrations occurred in the lensarrangement shown in FIG. 5 at the long focal length extremity;

[0034]FIG. 9 is a lens arrangement of a zoom lens system according to athird embodiment of the present invention;

[0035]FIGS. 10A, 10B and 10C show aberrations occurred in the lensarrangement shown in FIG. 9 at the short focal length extremity;

[0036]FIGS. 11A, 11B and 11C show aberrations occurred in the lensarrangement shown in FIG. 9 at an intermediate focal length;

[0037]FIGS. 12A, 12B and 12C show aberrations occurred in the lensarrangement shown in FIG. 9 at the long focal length extremity;

[0038]FIG. 13 is a lens arrangement of a zoom lens system according to afourth embodiment of the present invention;

[0039]FIGS. 14A, 14B and 14C show aberrations occurred in the lensarrangement shown in FIG. 13 at the short focal length extremity;

[0040]FIGS. 15A, 15B and 15C show aberrations occurred in the lensarrangement shown in FIG. 13 at an intermediate focal length;

[0041]FIGS. 16A, 16B and 16C show aberrations occurred in the lensarrangement shown in FIG. 13 at the long focal length extremity;

[0042]FIG. 17 is a lens arrangement of a zoom lens system according to afifth embodiment of the present invention;

[0043]FIGS. 18A, 18B and 18C show aberrations occurred in the lensarrangement shown in FIG. 17 at the short focal length extremity;

[0044]FIGS. 19A, 19B and 19C show aberrations occurred in the lensarrangement shown in FIG. 17 at an intermediate focal length;

[0045]FIGS. 20A, 20B and 20C show aberrations occurred in the lensarrangement shown in FIG. 17 at the long focal length extremity;

[0046]FIG. 21 is a lens arrangement of a zoom lens system according to asixth embodiment of the present invention;

[0047]FIGS. 22A, 22B and 22C show aberrations occurred in the lensarrangement shown in FIG. 21 at the short focal length extremity;

[0048]FIGS. 23A, 23B and 23C show aberrations occurred in the lensarrangement shown in FIG. 21 at an intermediate focal length;

[0049]FIGS. 24A, 24B and 24C show aberrations occurred in the lensarrangement shown in FIG. 21 at the long focal length extremity;

[0050]FIG. 25 is a lens arrangement of a zoom lens system according to aseventh embodiment of the present invention;

[0051]FIGS. 26A, 26B and 26C show aberrations occurred in the lensarrangement shown in FIG. 25 at the short focal length extremity;

[0052]FIGS. 27A, 27B and 27C show aberrations occurred in the lensarrangement shown in FIG. 25 at an intermediate focal length;

[0053]FIGS. 28A, 28B and 28C show aberrations occurred in the lensarrangement shown in FIG. 25 at the long focal length extremity;

[0054]FIG. 29 is a lens arrangement of a zoom lens system according toan eighth embodiment of the present invention;

[0055]FIGS. 30A, 30B and 30C show aberrations occurred in the lensarrangement shown in FIG. 29 at the short focal length extremity;

[0056]FIGS. 31A, 31B and 31C show aberrations occurred in the lensarrangement shown in FIG. 29 at an intermediate focal length; and

[0057]FIGS. 32A, 32B and 32C show aberrations occurred in the lensarrangement shown in FIG. 29 at the long focal length extremity.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] As shown in the lens arrangements of FIGS. 1, 5, 9, 13, 17, 21,25 and 29, the zoom lens system includes at least two lens groups, andthe negative first lens group 10 is positioned at the most object-sideof the zoom lens system, i.e., the zoom lens system according to thepresent invention is a negative-lead type zoom lens system.

[0059] More specifically, the embodiments of FIGS. 1, 5, 9 and 13 areapplied to a two-lens-group arrangement; and the embodiments of FIGS.17, 21, 25 and 29 are applied to a four-lens-group arrangement. Here,note that in each embodiment, the most object-side lens group has anegative power.

[0060] The negative first lens group 10 includes a negative firstsub-lens group 1A and positive second sub-lens group 1B, in this orderfrom the object. The positive second sub-lens group 1B includes apositive lens element 1B-1, and a lens element 1B-2 which is therearmost plastic lens element of the negative first lens group 10, inthis order from the object. Note that the rearmost plastic lens element1B-2 has at least one aspherical surface thereon. The zoom lens systemsatisfies conditions (1), (2) and (3).

[0061] In a zoom lens system of this type, if an aspherical surface isnot employed, the negative first lens group generally includes apositive lens element, a negative lens element, and a positive lenselement, in this order from the object. The correcting of distortion isperformed by providing a positive lens element at the most object-sideof the negative first lens group.

[0062] On the other hand, in the embodiments of the present invention,the most object-side sub-lens group is provided as a negative sub-lensgroup; and an aspherical surface is provided on the rearmost plasticlens element 1B-2 which has the smallest diameter among the lenselements of the negative first lens group 10. This arrangement iseffective in correcting distortion; and the diameter of the negativefirst lens group 10 can be made smaller, the overall length of the zoomlens system can be made shorter, and the cost thereof can also bereduced.

[0063] Condition (1) specifies the ratio of the power of the negativefirst lens group 10 to the power of the rearmost lens element (plasticaspherical lens element) 1B-2.

[0064] If |f₁/f_(1B-2) exceeds the upper limit of condition (1), thepower of the rearmost lens element 1B-2 becomes too strong, and theoptical performance of the lens element largely deteriorates withrespect to a change in temperature and humidity.

[0065] Condition (2) specifies the thickness of the rearmost lenselement (plastic aspherical lens element) 1B-2 of the negative firstlens group 10.

[0066] If D_(1B-2)/fw exceeds the lower limit of condition (2), themolding of the rearmost lens element 1B-2 becomes difficult, and cannotbe molded with a sufficient precision determined at the design stagethereof.

[0067] If D_(1B-2)/fw exceeds the upper limit of condition (2), the sizeof the negative first lens group 10 increases, so that furtherminiaturization cannot be achieved.

[0068] Condition (3) specifies the distance between the positive lenselement 1B-1 and the rearmost lens element (plastic aspherical lenselement) 1B-2 of the positive second sub-lens group 1B.

[0069] If D_(B1-B2)/fw exceeds the lower limit of condition (3), thereis a possibility that the positive lens element 1B-1 interferes with therearmost lens element 1B-2 due to manufacture error.

[0070] If D_(B1-B2)/fw exceeds the upper limit of condition (3), thesize of the negative first lens group 10 increases, so that furtherminiaturization becomes difficult.

[0071] In regard to the rearmost lens element 1B-2, in the case wherethe aspherical surface is formed on the object-side surface thereof, theaspherical surface indicates asphericity in the positive direction fromthe paraxial spherical surface; and in the case where the asphericalsurface is formed on the image-side surface thereof, the asphericalsurface indicates asphericity in the negative direction from theparaxial spherical surface. Due to these characteristics of asphericity,the positive power around the periphery of the lens element can be madestronger, so that negative distortion (barrel-type distortion) can becorrected, compared with the case where a spherical lens element isused.

[0072] Condition (4) determines a numerical value indicating the effectson the correcting of distortion by the aspherical surface at the shortfocal length extremity.

[0073] If ΔV exceeds the lower limit of condition (4), distortion isunder-corrected.

[0074] If ΔV exceeds the upper limit of condition (4), rearwarddistortion increases, the returning-amount of distortion defined belowbecomes larger.

[0075] The returning-amount of distortion is the difference between themaximum value of distortion and distortion at the maximum image height,under the condition that distortion is maximum at an intermediate areabetween the central area of the image plane and the periphery thereof,and that distortion at the periphery is smaller than distortion at theintermediate area.

[0076] Condition (5) is for the reduction in cost of the zoom lenssystem. If an attempt is made to use an inexpensive glass materialhaving a refractive index of 1.66 or less for at least one negative lenselement of the negative sub-lens group 1A in the negative first lensgroup 10 so that condition (5) is satisfied, the, cost of the zoom lenssystem can be reduced.

[0077] If N1A exceeds the upper limit of condition (5), the cost for thematerial is increased, so that further cost reduction becomes difficult.

[0078] The plastic aspherical lens element is employed for the rearmostlens element 1B-2 of the negative first lens group 10 because therearmost lens element 1B-2 has the smallest diameter, as explained, inthe negative first lens group 10. Moreover, it should be noted that theplastic aspherical lens element is easy to be replaced, if any problemoccurs.

[0079] In the diagrams of chromatic aberration (axial chromaticaberration) represented by spherical aberration, the solid line and thetwo types of dotted lines respectively indicate spherical aberrationswith respect to the d, g and C lines. Also, in the diagrams of lateralchromatic aberration, the two types of dotted lines respectivelyindicate magnification with respect to the g and C lines; however, the dline as the base line coincides with the ordinate. In the diagrams ofastigmatism, S designates the sagittal image, and M designates themeridional image. In the tables, FNO designates the f-number, fdesignates the focal length of the entire zoom lens system, fBdesignates the back focal distance, W designates the half angle-of-view(°), r designates the radius of curvature, d designates the lens-elementthickness or distance between lens elements, Nd designates therefractive index of the d-line, and νd designates the Abbe number.

[0080] In addition to the above, an aspherical surface which issymmetrical with respect to the optical axis is defined as follows:

x=cy ²/(1+[1−{1+K }c ² y ²]^(1/2))+A4y⁴ +A6y⁶ +A8y⁸ +A10y¹⁰ . . .

[0081] wherein:

[0082] c designates a curvature of the aspherical vertex (1/r);

[0083] y designates a distance from the optical axis;

[0084] K designates the conic coefficient; and

[0085] A4 designates a fourth-order aspherical coefficient;

[0086] A6 designates a sixth-order aspherical coefficient;

[0087] A8 designates a eighth-order aspherical coefficient; and

[0088] A10 designates a tenth-order aspherical coefficient.

[0089] The relationship between the aspherical coefficients andaberration coefficients are as follows:

[0090] 1. The shape of an aspherical surface is defined as follows:

x=cy ²/(1+[1−{1+K}c ² y ²]^(1/2))+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰ . . .

[0091] wherein:

[0092] x designates a distance from a tangent plane of an asphericalvertex;

[0093] y designates a distance from the optical axis;

[0094] c designates a curvature of the aspherical vertex (1/r),

[0095] K designates a conic constant;

[0096] 2. In this equation, to obtain the aberration coefficients, thefollowing substitution is made to replace K with “0”(Bi=Ai when K=0).

B4=A4+Kc ³/8;

B6=A6+(K ²+2K)c ⁵/16;

B8=A8+5(K ³+3K ²+3K)c ⁷/128

B10=A10+7(K ⁴+4K ³+6K ²+4K)c ⁹/256; and therefore, the followingequation is obtained:

x=cy ²/[1+[1−c ² y ²]^(1/2) ]+B4y ⁴ +B6y ⁶ +B8y ⁸ +B10y ¹⁰ . . .

[0097] 3. Furthermore, in order to normalize the focal length f to 1.0,the followings are considered:

X=x/f; Y=y/f; C=f*c;

α4=f ³ B4; α6=f ⁵ B6; α8=f ⁷ B8; α10=f ⁹ B10

[0098] Accordingly, the following equation is obtained.

X=CY ²/[1+[1−C ² Y ²]^(1/2)]+α4Y ⁴+α6Y ⁶+α8Y ⁸+α10Y ¹⁰+ . . .

[0099] 4. Φ=8(N′−N)α4 is defined, and the third aberration coefficientsare defined as follows:

[0100] I designates the spherical aberration coefficient;

[0101] II designates the coma coefficient;

[0102] III designates the astigmatism coefficient;

[0103] IV designates the curvature coefficient of the sagittal imagesurface; and

[0104] V designates the distortion coefficient; and therefore, theinfluence of the fourth-order aspherical-surface coefficient (α4) oneach aberration coefficient is defined as:

ΔI=h ⁴Φ

ΔII=h ³ kΦ

ΔIII=h ² k ²Φ

ΔIV=h ² k ²Φ

ΔV=hk ³Φ

[0105] wherein

[0106] h1 designates the height at which a paraxial axial light raystrikes the first surface of the lens system including the asphericalsurface;

[0107] h designates the height at which the paraxial axial light raystrikes the aspherical surface when the height h1 is 1;

[0108] k1 designates the height at which a paraxial off-axis ray,passing through the center of the entrance pupil, strikes the firstsurface of the lens system including the aspherical surface;

[0109] k designates the height at which the paraxial off-axis light raystrikes the aspherical surface when the height k1 is −1;

[0110] N′ designates the refractive index of a medium on the side of theimage with respect to the aspherical surface; and

[0111] N designates the refractive index of a medium on the side of theobject with respect to the aspherical surface.

[0112] [Embodiment 1]

[0113]FIG. 1 is the lens arrangement of a zoom lens system according tothe first embodiment of the present invention. FIGS. 2A through 2C showaberrations occurred in the lens arrangement shown in FIG. 1 at theshort focal length extremity. FIGS. 3A through 3C show aberrationsoccurred in the lens arrangement shown in FIG. 1 at an intermediatefocal length. FIGS. 4A through 4C show aberrations occurred in the lensarrangement shown in FIG. 1 at the long focal length extremity. Table 1shows the numerical values of the first embodiment.

[0114] The zoom lens system of the first embodiment includes a negativefirst lens group 10, a second lens group 20 on which a diaphragm S ismounted, and a flare-cut diaphragm S′, in this order from the object.

[0115] The negative first lens group 10 includes a meniscus lens element11 having the convex surface facing toward the object, a meniscus lenselement 12 having the convex surface facing toward the object, apositive meniscus lens element 1B−1 having the convex surface facingtoward the object, and a rearmost lens element 1B−2 having an asphericalsurface on the image-side surface thereof, in this order from theobject.

[0116] The second lens group 20 includes a biconvex lens element 21, ameniscus lens element 22 having the convex surface facing toward theobject, a diaphragm S, a biconcave lens element 23, and a biconvex lenselement 24, in this order from the object.

[0117] Upon zooming from the short focal length extremity (wide-angleextremity) W to the long focal length extremity (telephoto extremity) T,as shown in the lens-group moving paths of FIG. 1, the negative firstlens group 10 moves first toward the image and then toward the object,and the second lens group 20 and the flare-cut diaphragm S′ eachindependently move monotonously toward the object. TABLE 1 FNO. =1:3.3-4.0-5.9 f = 29.00-40.65-77.00 (Zoom Ratio: 2.66) W =38.2-28.4-15.7 fB = 44.95-55.2-87.21 D8 = 32.48-18.10-1.20

[0118] Diaphragm Position:

[0119] 1.50 behind surface No. 12

[0120] Flare-Cut Diaphragm Position

[0121] Behind surface No. 16 0.4−3.4−12.7 Surface No. r d Nd νd 1 51.3411.20 1.70154 41.2 2 18.959 5.60 — — 3 40.514 1.00 1.64850 53.0 4 20.9274.22 — — 5 33.704 4.02 1.78472 25.7 6 102.710 0.20 — — 7 93.259 1.801.52538 56.3  8* 57.389 D8 — — 9 32.433 2.83 1.61272 58.7 10  −1700.3640.10 — — 11  21.428 3.08 1.61405 55.0 12  80.609 2.83 — — 13  −143.5856.75 1.71736 29.5 14  16.357 1.04 — — 15  29.457 5.00 1.51742 52.4 16 −35.348 — — —

[0122] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 A10 A12 8 0.00 −0.15736× 10⁻⁴ −0.25379 × 10⁻⁷ 0.24583 × 10⁻¹⁰ −0.35828 × 10⁻¹² 0.33124 × 10⁻¹⁵

[0123] [Embodiment 2]

[0124]FIG. 5 is the lens arrangement of a zoom lens system according tothe second embodiment of the present invention. FIGS. 6A through 6C showaberrations occurred in the lens arrangement shown in FIG. 5 at theshort focal length extremity. FIGS. 7A through 7C show aberrationsoccurred in the lens arrangement shown in FIG. 5 at an intermediatefocal length. FIGS. 8A through 8C show aberrations occurred in the lensarrangement shown in FIG. 5 at the long focal length extremity. Table 2shows the numerical values of the second embodiment. The basic lensarrangement and the lens-group moving path of each lens group uponzooming is the same as the first embodiment. TABLE 2 FNO. =1:3.3-4.0-5.9 f = 29.00-40.65-77.00 (Zoom Ratio: 2.66) W =38.2-28.4-15.7 fB = 43.97-54.06-85.57 D8 = 31.97-17.83-1.20

[0125] Diaphragm Position:

[0126] 1.50 behind surface No. 12

[0127] Flare-Cut Diaphragm Position

[0128] Behind surface No. 16 0.5−3.2−11.7 Surface No. r d Nd νd 1 50.9641.20 1.72342 38.0 2 19.092 5.48 — — 3 39.411 1.00 1.60311 60.7 4 20.3394.15 — — 5 32.831 4.11 1.78472 25.7 6 100.706 0.20 — — 7 91.600 1.801.52538 56.3  8* 52.697 D8 — — 9 30.488 2.98 1.62299 58.2 10  −1378.4140.10 — — 11  19.895 3.33 1.56883 56.3 12  76.761 2.81 — — 13  −153.4875.58 1.71736 29.5 14  15.603 1.15 — — 15  29.769 5.00 1.51742 52.4 16 −36.095 — — —

[0129] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 A10 A12 8 0.00 −0.16147× 10⁻⁴ −0.26675 × 10⁻⁷ 0.13573 × 10⁻¹⁰ −0.32468 × 10⁻¹² 0.18136 × 10⁻¹⁵

[0130] [Embodiment 3]

[0131]FIG. 9 is the lens arrangement of a zoom lens system according toa third embodiment of the present invention. FIGS. 10A through 10C showaberrations occurred in the lens arrangement shown in FIG. 9 at theshort focal length extremity. FIGS. 11A through 11C show aberrationsoccurred in the lens arrangement shown in FIG. 9 at an intermediatefocal length. FIGS. 12A through 12C show aberrations occurred in thelens arrangement shown in FIG. 9 at the long focal length extremity.Table 3 shows the numerical values of the third embodiment. The basiclens arrangement and the lens-group moving path of each lens groupduring zooming is the same as the first embodiment. TABLE 3 FNO. =1:3.3-4.0-5.9 f = 29.00-41.29-77.00 (Zoom Ratio: 2.66) W =38.2-28.4-15.7 fB = 44.43-55.09-86.07 D8 = 33.02-17.83-1.20

[0132] Diaphragm Position:

[0133] 1.50 behind surface No. 12

[0134] Flare-Cut Diaphragm Position

[0135] Behind surface No. 16 0.93−3.8−12.8 Surface No. r d Nd νd 150.042 1.20 1.70154 41.2 2 21.212 5.93 — — 3 65.233 1.00 1.64850 53.0 421.292 4.68 — — 5 32.593 3.77 1.78472 25.7 6 74.551 0.10 — — 7 65.1532.10 1.52538 56.3  8* 65.239 D8 — — 9 33.142 2.77 1.61272 58.7 10 −2864.281 0.10 — — 11  20.570 3.12 1.61405 55.0 12  70.039 3.05 — — 13 −176.367 6.69 1.71736 29.5 14  15.933 0.84 — — 15  27.987 4.74 1.5174252.4 16  −37.532 — — —

[0136] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 A10 A12 8 0.00 −0.10293× 10⁻⁴ −0.21736 × 10⁻⁷ 0.65859 × 10⁻¹⁰ −0.35672 × 10⁻¹² 0.33528 × 10⁻¹⁵

[0137] [Embodiment 4]

[0138]FIG. 13 is the lens arrangement of a zoom lens system according toa fourth embodiment of the present invention. FIGS. 14A through 14C showaberrations occurred in the lens arrangement shown in FIG. 13 at theshort focal length extremity. FIGS. 15A through 15C show aberrationsoccurred in the lens arrangement shown in FIG. 13 at an intermediatefocal length. FIGS. 16A through 16C show aberrations occurred in thelens arrangement shown in FIG. 13 at the long focal length extremity.Table 4 shows the numerical values of the fourth embodiment. The basiclens arrangement and the lens-group moving path of each lens groupduring zooming is the same as the first embodiment. TABLE 4 FNO. =1:3.3-3.9-5.9 f = 29.00-40.00-77.00 (Zoom Ratio: 2.66) W =38.2-28.9-15.7 fB = 44.75-54.48-87.20 D8 = 32.05-18.44-1.20

[0139] Diaphragm Position:

[0140] 1.50 behind surface No. 12

[0141] Flare-Cut Diaphragm Position

[0142] Behind surface No. 16 1.5−4.2−13.0 Surface No. r d Nd νd 1 47.8441.20 1.70154 41.2 2 18.707 5.66 — — 3 39.070 1.00 1.64850 53.0 4 20.8974.40 — — 5 33.504 4.04 1.78472 25.7 6 101.702 0.70 — — 7 147.257 1.201.52538 56.3  8* 63.661 D8 — — 9 31.958 2.88 1.61272 58.7 10  −1198.5580.10 — — 11  21.794 3.07 1.61405 55.0 12 85.230 2.82 — — 13 −136.9556.93 1.71736 29.5 14 16.359 1.08 — — 15 29.478 5.00 1.51742 52.4 16−35.372 — — —

[0143] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 8 0.00 −0.15075 × 10⁻⁴−0.29128 × 10⁻⁷ A8 A10 A12 0.48383 × 10⁻¹⁰ −0.37091 × 10⁻¹² 0.25160 ×10⁻¹⁵

[0144] [Embodiment 5]

[0145]FIG. 17 is the lens arrangement of a zoom lens system according tothe fifth embodiment of the present invention. FIGS. 18A through 18Cshow aberrations occurred in the lens arrangement shown in FIG. 17 atthe short focal length extremity. FIGS. 19A through 19C show aberrationsoccurred in the lens arrangement shown in FIG. 17 at an intermediatefocal length. FIGS. 20A through 20C show aberrations occurred in thelens arrangement shown in FIG. 17 at the long focal length extremity.Table 5 shows the numerical values of the fifth embodiment.

[0146] The zoom lens system of the fifth embodiment includes a negativefirst lens group 10, a second lens group 20, a diaphragm S, a third lensgroup 30, and a fourth lens group 40, in this order from the object.Unlike the first through fourth embodiments, a flare-cut diaphragm isnot provided.

[0147] The negative first lens group 10 includes a meniscus lens element11 having the convex surface facing toward the object, a meniscus lenselement 12 having the convex surface facing toward the object, apositive meniscus lens element 1B-1 having the convex surface facingtoward the object, and a rearmost lens element 1B-2 having an asphericalsurface on the image-side surface thereof, in this order from theobject.

[0148] The second lens group 20 includes a biconvex lens element 25,cemented lens elements having a biconvex lens element 26 and a biconcavelens element 27, in that order from the object side.

[0149] The third lens group 30 includes cemented lens elements having ameniscus lens element 31 having the convex surface facing toward theimage and a biconcave lens element 32.

[0150] The fourth lens group 40 includes a biconvex lens element 41 anda meniscus lens element 42 having the convex surface facing toward theimage, in this order from the object

[0151] Upon zooming from the short focal length extremity (wide-angleextremity) W to the long focal length extremity (telephoto extremity) T,as shown in the lens-group moving paths of FIG. 17, the negative firstlens group 10 moves first toward the image and then toward the object;and the second lens group 20, the third lens group 30 and the fourthlens group 40 each independently move monotonously toward the object.TABLE 5 FNO. = 1:3.6-4.5-5.9 f = 29.00-52.93-87.00 (Zoom Ratio: 3.00) W= 38.1-22.0-13.7 fB = 36.70-52.46-73.02 D8 = 35.76-12.08-1.35 D13 =3.30-6.38-10.03 D16 = 7.48-5.27-1.36

[0152] Diaphragm Position:

[0153] 1.5 behind surface No. 14 Surface No. r d Nd νd  1 65.072 1.201.60311 60.7  2 19.951 8.83 — —  3 116.727 1.50 1.67790 55.3  4 35.2170.70 — —  5 38.618 3.50 1.84666 23.8  6 91.125 0.20 — —  7 63.982 3.001.58547 29.9  8* 47.372 D8  — —  9 25.175 4.45 1.58913 61.2 10 −57.6160.10 — — 11 31.872 4.64 1.51742 52.4 12 −28.042 1.00 1.80518 25.4 13236.003 D13 — — 14 −108.075 7.29 1.80518 25.4 15 −14.004 1.00 1.8061040.9 16 37.963 D16 — — 17 4509.489 3.40 1.77250 49.6 18 −20.247 0.90 — —19 −15.178 1.00 1.80518 25.4 20 −26.738 — — —

[0154] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 8 0.00 −0.69482 × 10⁻⁵−0.30673 × 10⁻⁸ −0.35008 × 10⁻¹⁰

[0155] [Embodiment 6]

[0156]FIG. 21 is the lens arrangement of a zoom lens system according toa sixth embodiment of the present invention. FIGS. 22A through 22C showaberrations occurred in the lens arrangement shown in FIG. 21 at theshort focal length extremity. FIGS. 23A through 23C show aberrationsoccurred in the lens arrangement shown in FIG. 21 at an intermediatefocal length. FIGS. 24A through 24C show aberrations occurred in thelens arrangement shown in FIG. 21 at the long focal length extremity.Table 6 shows the numerical values of the sixth embodiment.

[0157] The zoom lens system of the sixth embodiment is the same as thefifth embodiment except that the lens element 43 of the fourth lensgroup 40 is a meniscus lens element having the convex surface facingtoward the image. The lens-group moving paths of each lens group uponzooming is the same as the fifth embodiment. TABLE 6 FNO. =1:3.5-4.5-5.9 f = 29.00-52.89-87.00 (Zoom Ratio: 3.00) W =38.2-22.0-13.7 fB = 36.70-52.90-73.70 D8 = 34.92-11.67-1.35 D13 =4.57-7.59-11.24 D16 = 8.01-4.99-1.34

[0158] Diaphragm Position:

[0159] 1.5 behind surface No. 14 Surface No. r d Nd νd  1 66.274 1.201.60311 60.7  2 20.174 8.86 — —  3 128.303 1.50 1.67790 55.3  4 38.0460.70 — —  5 35.956 3.50 1.84666 23.8  6 69.757 0.20 — —  7 60.695 2.001.52538 56.3  8* 44.562 D8  — —  9 25.001 4.46 1.58913 61.2 10 −55.0160.10 — — 11 31.210 4.65 1.51742 52.4 12 −27.089 1.00 1.80518 25.4 13167.329 D13 — — 14 −81.962 4.48 1.80518 25.4 15 −14.000 1.00 1.8061040.9 16 41.231 D16 — — 17 −4585.308 3.37 1.77250 49.6 18 −20.293 1.15 —— 19 −15.095 1.00 1.80518 25.4 20 −24.749 — — —

[0160] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 8 0.00 −0.58550 × 10⁻⁵−0.20789 × 10⁻⁸ −0.27939 × 10⁻¹⁰

[0161] [Embodiment 7]

[0162]FIG. 25 is the lens arrangement of a zoom lens system according tothe seventh embodiment of the present invention. FIGS. 26A through 26Cshow aberrations occurred in the lens arrangement shown in FIG. 25 atthe short focal length extremity. FIGS. 27A through 27C show aberrationsoccurred in the lens arrangement shown in FIG. 25 at an intermediatefocal length. FIGS. 28A through 28C show aberrations occurred in thelens arrangement shown in FIG. 25 at the long focal length extremity.Table 7 shows the numerical values of the seventh embodiment.

[0163] The zoom lens system of the seventh embodiment is the same as thesixth embodiment except that the rearmost lens element 1B-2 is providedwith an aspherical surface on the object-side surface thereof. Thelens-group moving paths of each lens group upon zooming is the same asthe sixth embodiment. TABLE 7 FNO. = 1:3.5-4.5-5.9 f = 29.00-52.85-87.00(Zoom Ratio: 3.00) W = 38.1-22.0-13.7 fB = 36.70-52.79-73.77 D8 =34.82-11.65-1.35 D13 = 5.07-8.08-11.70 D16 = 7.91-5.32-1.34

[0164] Diaphragm Position:

[0165] 1.5 mm behind surface No. 14 Surface No. r d Nd νd  1 62.862 1.201.60311 60.7  2 20.959 8.91 — —  3 218.908 1.50 1.67790 55.3  4 36.1791.18 — —  5 34.154 3.50 1.84666 23.8  6 69.896 0.20 — —  7* 61.265 1.501.58547 29.9  8 46.220 D8  — —  9 25.294 4.44 1.58913 61.2 10 −54.8110.10 — — 11 30.668 4.64 1.51742 52.4 12 −28.088 1.00 1.80518 25.4 13175.833 D13 — — 14 −67.968 4.05 1.80518 25.4 15 −14.000 1.00 1.8061040.9 16 42.304 D16 — — 17 −743.698 3.37 1.77250 49.6 18 −20.010 1.14 — —19 −14.826 1.00 1.80518 25.4 20 −23.413 — — —

[0166] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 7 0.00 0.30142 × 10⁻⁵−0.72479 × 10⁻¹⁰ 0.87347 × 10⁻¹¹

[0167] [Embodiment 8]

[0168]FIG. 29 is the lens arrangement of a zoom lens system according toan eighth embodiment of the present invention. FIGS. 30A through 30Cshow aberrations occurred inthe lens arrangement shown in FIG. 29 at theshort focal length extremity. FIGS. 31A through 31C show aberrationsoccurred in the lens arrangement shown in FIG. 29 at an intermediatefocal length. FIGS. 32A through 32C show aberrations occurred in thelens arrangement shown in FIG. 29 at the long focal length extremity.Table 8 shows the numerical values of the eighth embodiment.

[0169] The zoom lens system of the eighth embodiment and the lens-groupmoving path of each lens group upon zooming is the same as the seventhembodiment. TABLE 8 FNO. = 1:3.5-4.5-5.9 f = 29.00-52.85-87.00 (ZoomRatio: 3.00) W = 38.1-22.0-13.7 fB = 36.70-52.79-73.37 D8 =34.82-11.65-1.35 D13 = 5.07-8.08-11.70 D16 = 7.91-5.32-1.34

[0170] Diaphragm Position:

[0171] 1.5 behind surface No. 14 Surface No. r d Nd νd 1 62.862 1.201.60311 60.7 2 20.959 8.91 — — 3 218.908 1.50 1.67790 55.3 4 36.179 1.18— — 5 34.154 3.50 1.84666 23.8 6 69.896 0.20 — —  7* 61.265 1.50 1.5854729.9 8 46.220 D8  — — 9 25.294 4.44 1.58913 61.2 10  −54.811 0.10 — —11  30.668 4.64 1.51742 52.4 12  −28.088 1.00 1.80518 25.4 13  175.833D13 — — 14  −67.968 4.05 1.80518 25.4 15  −14.000 1.00 1.80610 40.9 16 42.304 D16 — — 17  −743.698 3.37 1.77250 49.6 18  −20.010 1.14 — — 19 −14.826 1.00 1.80518 25.4 20  −23.413 — — —

[0172] Aspherical surface data (the aspherical surface coefficients notindicated are zero (0.00)): Surf. No. K A4 A6 A8 7 0.00 0.30142 × 10⁻⁵−0.72479 × 10⁻¹⁰ 0.87347 × 10⁻¹¹

[0173] Table 9 shows the numerical values of each condition for eachembodiment. TABLE 9 Embod. 1 Embod. 2 Embod. 3 Embod. 4 Cond. (1) 0.140.17 0.004 0.19 Cond. (2) 0.062 0.062 0.072 0.041 Cond. (3) 0.007 0.0070.003 0.024 Cond. (4) −0.43 −0.44 −0.29 −0.40 Cond. (5) 1.6485 1.603111.6485 1.6485 Embod. 5 Embod. 6 Embod. 7 Embod. 8 Cond. (1) 0.116 0.1160.115 0.115 Cond. (2) 0.103 0.069 0.052 0.052 Cond. (3) 0.007 0.0070.007 0.007 Cond. (4) −0.28 −0.23 −0.15 −0.15 Cond. (5) 1.60311 1.603111.60311 1.60311

[0174] As can be understood from the Table 9, each embodiment satisfieseach condition of the present invention, and as can be understood fromthe drawings, the various aberrations can be adequately corrected.

[0175] According to the above description, a miniaturized and low-costzoom lens system having a half angle-of-view of 38° at the short focallength extremity, and having a zoom ratio of approximately 3 can beobtained.

What is claimed is:
 1. A zoom lens system comprising at least two lens groups, wherein a negative first lens group is positioned at the most object-side of said zoom lens system; wherein said negative first lens group comprises a negative sub-lens group and a positive sub-lens group, in this order from an object; wherein said positive sub-lens group comprises a positive lens element and a rearmost lens element of said negative first lens group, in this order from said object; wherein said rearmost lens element comprises a plastic lens element having at least one aspherical surface; and wherein said zoom lens system satisfies the following conditions: |f ₁ /f _(1B-2)|<0.3 0.02<D _(1B-2) /fw<0.2 0.001<D _(B1-B2) /fw<0.1 wherein f₁ designates the focal length of said negative first lens group; f_(1B-2) designates the focal length of said rearmost lens element of said negative first lens group; fw designates the focal length of the entire the zoom lens system at the short focal length extremity; D_(1B-2) designates the thickness of said rearmost lens element of said negative first lens group; and D_(B1-B2) designates the distance between said positive lens element and said rearmost lens element in said positive sub-lens group.
 2. The zoom lens system according to claim 1, wherein said aspherical surface of said rearmost lens element is provided on the object-side surface thereof, and said aspherical surface is formed so that the positive power becomes stronger, compared with a paraxial spherical surface, in a direction away from the optical axis.
 3. The zoom lens system according to claim 1, wherein said aspherical surface of said rearmost lens element is provided on the image-side surface thereof, and said aspherical surface is formed so that the positive power becomes stronger, compared with a paraxial spherical surface, in a direction away from the optical axis.
 4. The zoom lens system according to claim 1, wherein said aspherical surface of said rearmost lens element of said negative first lens group satisfies the following condition: −1<ΔV<−0.1 wherein ΔV designates the amount of change of the distortion coefficient due to said aspherical surface of said rearmost lens element of said negative first lens group under the condition that the focal length at the short focal length extremity is converted to 1.0.
 5. The zoom lens system according to claim 1, wherein a refractive index N_(1A) of a glass material of at least one negative lens element of said negative object-side sub-lens group in said negative first lens group satisfies the following condition: N _(1A)<1.66 